Transcript Short grass minus Forest

Lecture 7 S. American Climate
• Physical Settings
• Circulation controls
• Climate Change — Impacts of
Amazonian Deforestation
Topography
Like Africa, primarily a
tropical continent
Distinguish characteristic is
the unbroken, high Andes
Mt. chain that run the entire
length near its west coast —
allow the greatest
meridional penetration of air
masses anywhere in the S.H.
Continent extends farther
poleward than any other S.H.
continents — 56S, coming
within 7 degree of Antarctic
peninsula
fT
mT
mT
The Guiana current is fed by the North Brazil
Current a major source of water for the Caribbean
Sea. Water transported by the Guiana current also
mixes with tropical waters from the N. Equatorial
Current and eventually feeds the circulation of the
N. Atlantic subtropical Gyre, via the Caribbean,
Yucatan, Loop, and Florida currents.
The N. Brazil current transports a significant amount
of water, including freshwater from the Amazon,
northwestward along the coast of northern Brazil,
French Guiana, and Suriname. It is fed by the S.
Equatorial Current and part of it becomes the Guiana
Current.
The Brazil current is the western boundary
current of the South Atlantic subtropical gyre.
Near 22 S, the Brazil current splits; one component
flows eastward and the other component hugs the
coast and flows toward the southwest and interacts
with the colder Malvinas Current.
The Malvinas current is the northward flow component of
the S. Atlantic subpolar gyre. It transports cold water
along the coast of S. America and this water mixes with
warmer waters of the Brazil current in an region known as
the Brazil-Malvinas confluence.
The Peru Current (or Humboldt Current) is a cold ocean current that flows
northward off the west coast of S.A. It becomes a major part of the westward South
Equatorial Current. This current originates in the Southern Ocean near the Antarctic,
and is thus about 7-8 C° cooler than the ocean at similar latitudes. The cold water
cools down the air, creating the coastal deserts of Chile: the Atacama and Peru.
However, the Humbolt Current brings nutrient-rich seawater into the region, forming
the basis for a rich fishing industry on Peru and Chile.
MAIN FISHERY RESOURCES
PELAGIC
SARDINE
ANCHOVY
PACIFIC MACKEREL
JACK MACKEREL
LIGHTFISH
DEMERSAL
HAKE
INVERTEBRATES
JUMBO FLYING
SQUID
PERUVIAN
SCALLOP
Baron Alexander von Humboldt (September 14, 1769-May 6, 1859) was a Prussian naturalist and
explorer who explored much of Central and South America. Humboldt and his friend, the French
medical doctor/botanist Aime-Jacques-Alexandre Goujoud Bonpland (1773-1858), explored the coast
of Venezuela, the Amazon and Orinoco Rivers, and much of Peru, Ecuador, Colombia and Mexico
(1799-1805).
On their many expeditions, Humboldt and Bonpland collected plant, animal, and mineral specimens,
studied electricity (including discovering the first animal that produced electricity, Electrophorus
electricus, the electric eel), did extensive mapping of northern South America, climbed mountains (and
set altitude records), observed astronomical phenomena, and performed many scientific observations.
The scientist Carlos Montufar (who later became a revolutionary in Ecuador) acconpanied them on part
of the trip.
Humboldt discovered what is now called the Humboldt Current off the west coast of South America, while he was
investigating why the interior of Peru was so dry. It is a cold ocean current that runs along much of the western coast
of South America, and is also known as the Peru Current.
Humboldt was the first European to witness native South Americans preparing curare arrow poison from a vine. He
was also the first person to recognize the need to preserve the cinchona plant (its bark contains quinine, which is used
to cure malaria, and it was terribly over-harvested at the time). Humboldt was the first person to make accurate
drawings of Inca ruins in South America (he visited the ruins at Canar, Peru). Humboldt and Bonpland first discovered
and mapped the Casiquiare Canal, the only natural canal in the world that connects two major rivers (the Orinoco River
and the Negro River, a tributary of the Amazon). Humboldt was also the first person to discover the importance of
guano (the dried droppings from fish-eating birds); it is an excellent fertilizer.
After their South American expeditions, Humboldt and Bonpland visited the USA and were guests of President
Thomas Jefferson in Washington, D.C., for three months in 1804 (their visit happened just after Jefferson had sent
Lewis and Clark to explore the western US).
At the age of 60, Humboldt traveled to the Ural mountains in Siberia and to Central Asia to study the weather. He
wrote extensively of his travels and discoveries. One of his books, A Personal Narrative inspired a young Charles
Darwin. His last work was his multi-volume book, Kosmos, which tried to unify all of science. Humboldt died at age
90 (leaving Kosmos unfinished), and is buried in Tegel, Germany. Many landmarks in the Americas, including a
current, a river, a mountain range, a reservoir, a salt marsh, parks, many counties and towns are named for Humboldt.
On the moon, the Mare Humboldtianum (Humboldt's Sea) was named for Humboldt.
The cold currents around the Galapagos cause garua (mist) for part of the year. Early
sailors thought the islands were enchanted as a result of their frequent disappearance.
View of clouds over the ocean off Peru
Sunset over the southeastern Pacific from Paracas bay (14S, 76W), Peru.
Amazon rainforest, near Iquitos
Peru rainforest in eastern Peru
Altiplano plateau, Peru
Atacama desert, Chilean coast
Trewartha
Climatic
Classification
System
• Physical Settings
• Circulation controls
• Climate Change — Impacts of
Amazonian Deforestation
Chaco
Low
Positionally Stable Pacific Subtropical High
The shape of the west coast of S.A. forms a near-perfect “basin” into
which the S. Pacific STH can fit snugly and maintain contact with
the continent almost to the equator
No other STH is so positionally stable and so perfectly anchored
along a coast; produces maximum subsidence in the coastal area
Less “Unstable” Influences of Atlantic Subtropical High
To the east, air in the Cf region (Brazil) is not nearly as unstable as
that in the Cf region of N. America (i.e. SE of U.S.) due to
continent’s shape which bulges eastward into the influence of the
more stable part of the South Atlantic STH.
Unique
ITCZ
Behavior
Intrusion of
Cold Front
低層環流與降雨
Moisture sources of
La Plata basin of
southeastern S.A.
Mean calendar date of onset of South American monsoon
• Physical Settings
• Circulation controls
• Climate Change — Impacts of
Amazonian Deforestation
Title
Deforestation:
Rondonia, Brazil
Body text
•1975 -Healthy natural
vegetation
•1986 -“Fishbone”
pattern on the
landscape indicate
agriculture fields
Satellite images reveal in startling detail
the signs of human impact on the
landscape. Evidence that people have
become a powerful force capable of
reshaping the Earth’s environment is
everywhere.
•2000 -Agriculture
continues to replace
forest cover.
雨林消失對氣候的衝擊
1.改變蒸發蒸散作用的速率
2.改變其在碳循環中扮演的源與匯角色
3.改變區域水循環
逕流增加或減少?
亞馬遜河流域的熱帶
森林區，每年約有100
～200萬公頃的森林被
清除，多項研究已顯
示，如此高速率、大
規模砍燒森林會增加
大氣中CO2濃度，改變
當地的水文及氣候。
衛星照片顯示，東部
與南部是消退最快速
的地區，1978年森林
消退的面積是
78000km2，1988年達
到230000km2。
沒有控制與有控制的森林採伐所造成的 a.
地表溫度(C); b. 深土溫度(C);c. 總降水
量(mm);d. 蒸發量(mm)等的變化 ◦
Differences between simulated parameters:
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Decrease in
precipitation
Increase in
precipitation
Local temperature increase
reaching until 5°C
Differences between simulated parameters:
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The increase in maximum temperature is larger than
the increase in minimum temperature
Differences between simulated parameters:
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Ground Temperature
Foliage Temperature
Ground and foliage temperature is higher in the short
grass in the Amazon region, and is lower in other areas
Differences between simulated parameters:
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Dryer
Moister
Differences between simulated parameters:
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Over the
Amazon the
lower level
winds ( σ=1)
became more
intense in the
short grass